(Spoiler alert: Don't read this if you don't want to hear about tonight's "Justified" season finale. And check back in on Wednesday for a full interview with Graham Yost, who breaks down the third season and the finale.)

With Robert Quarles, "Justified" creator Graham Yost says he set out to create the ultimate opponent for U.S. marshal Raylan Givens — one audiences would despise so much that they wanted him dead.

"Not saying that Quarles is going to die!" said Yost (pictured on the left, above, with McDonough). "But, you know, I think the audience is rubbing their hands together a little bit, wondering 'How is this all going to play out?'"

McDonough has made Quarles — a Detroit mobster who came to Kentucky with dreams of becoming the new local drug lord — the latest in a long line of scene-stealing "Justified" criminals. Margo Martindale won an Emmy for her portrayal of Mags.

"I think we were always content on spinning him out of control and letting him get crazier and crazier," Yost says. "I would say maybe our first thought was not quite as crazy. I think our first thought was more (that he would be) dangerous and diabolical. We knew we wanted to paint him into a corner … and then he would get ever more dangerous the more cornered he became.

"But I think there were little things that Neal was doing early on that let us think that there was some place to go with, just, basic wackiness. And then when we came up with the thing, the boy chained to the bed (in "Guy Walks Into a Bar"), and we revealed (Quarles' backstory), that just gave us a whole new terrain to explore with him."

Also read:Timothy Olyphant on 'Justified' Season Finale: People Die in 'Unexpected, Wonderful Ways'

The inevitable Quarles/Raylan face-off is just one of the dramatic moments in the finale. Boyd (Walton Goggins) will find himself in a vulnerable position. Raylan (Timothy Olyphant) hears an unbelievable admission from his dad, Arlo (Raymond Barry). And Quarles faces off with the season's other big criminal, Ellstin Limehouse (Mykelti Williamson).

"The goal with Limehouse from the beginning was to have a character who was a big question mark," Yost says. "That you weren't sure … you know, he's a criminal, but is he a bad guy?"

One more spoiler alert: The season finale offers more fuel for that debate.